This invention is directed to a process of recovering petroleum from underground reservoirs.
Some of the largest known liquid petroleum deposits in the world are the Athabasca tar sands located in northern Alberta. Moreover, the high-viscosity crude petroleum in these oil sands is not recoverable in its natural state by ordinary in-situ methods. To date, none of these deposits has been produced commercially with much success, except by surface mining. Only two commercial mining operations exist, and they are in the shallow Athabasca deposits. Numerous processes have been employed in efforts to recover such material, including processes involving mining and centrifuging the tar sand in the presence of certain solvents and surface active agents, and subjecting the mined tar sand mixture to treatment with hot water to separate the resulting upper oil layer. These and other methods which have been used, however, all require large operational and capital expenditures.
In-situ technology as a means of commercially recovering Athabasca bitumen deposits of this type has never been employed However, there have been many in-situ well-to-well pilots, all of which have used some form of thermal recovery after establishing communication between an injector and a producer. Normally, such communication has been established by introducing a pancake fracture. The displacing or drive mechanism has been steam or combustion, such as the project at Gregoire Lake; or steam and chemicals, such as the early work on Lease 13 of the Athabasca deposit.
Another means of establishing communication is that proposed for the Peace River project. It is expected to develop well-to-well communication by injecting steam over a period of several years into an aquifer underlying the tar sand deposit at a depth of about 1800 feet.
Probably the most active in-situ commercial operation in the oil sands has been at Cold Lake. This project uses the huff-and-puff single-well method of steam stimulation and is producing about 88,000 barrels of viscous petroleum per day.
The most difficult problem in any in-situ well-to-well viscous petroleum project is establishing and maintaining communication between the injector and the producer. In shallow deposits, fracturing to the surface has occurred in a number of pilots so that satisfactory drive pressure and injectivity cannot be maintained. In typical steam applications, the produced oil flows from the hot zone through the unheated zone to the production well. In the heated zone, viscosity of the oil is at a minimum; however, as the pressure of the system forces the oil toward the producing well, the oil decreases in temperature to that of the unheated portion of the reservoir and mobility of the flowing oil decreases.
As noted, the major problem of the economic recovery from many formations has been establishing communications between an injection position and a recovery position in the viscous oil-containing formation. This is primarily due to the character of the formation, where oil mobility may be extremely low, and in some cases, such as the Athabasca tar sands, virtually nil. Thus, the Athabasca tar sands, for example, are strip mined where the overburden is limited. In some tar sands, hydraulic fracturing has been used to establish communication between injectors and producers. This, however, has not met with uniform success.
In-situ hydrogenation of heavy oils and tar sands based upon achieving hydrogenation temperatures by means of in-situ combustion has been used, but again, with little success. In order for hydrogenation to take place it is necessary to contact the oil with heat and hydrogen for a significant length of time so that enough of the reaction can take place to upgrade the oil so that it can be produced. In-situ combustion is a flow process and by its very nature tends to displace the oil in the formation. Thus, the temperature in the formation closest to the combustion zone is suitable for hydrogenation; however, the farther away from this area the more unlikely it is that the temperature conditions will promote hydrogenation, there presently exists no method for regulating temperature throughout the formation.
Heretofore, many processes have been utilized in attempting to recover viscous petroleum from viscous formations of the Athabasca tar sands type. The application of heat to such viscous petroleum formation by steam or underground combustion has been attempted. The use of slotted liners positioned in the viscous oil formation as a conduit for hot fluids has also been suggested. In-situ hydrogenation based upon achieving hydrogenation temperatures in the formation has also been tried. However, these methods have not been overly successful because of the difficulty of establishing and maintaining communication between the injector and the producer.
A solution to this problem of establishing communication between the injector and producer has been disclosed in U.S. Pat. Nos. 4,696,345; 4,460,044; 4,368,781; 4,303,126; 4,120,357; 4,037,658; 4,020,901; 4,019,575; 4,008,765; 3,994,341 and 3,994,340, which are incorporated by reference to show a HASDrive (Heated Annulus Steam Drive) method. None of these references disclose the addition of a hydrogen-generating or hydrogen-containing gas or a sufficient temperature being established in the formation to promote the hydrogenation and cracking of at least a portion of the petroleum in said formation zone. Nor do they disclose the addition of a catalyst into the formation.
In 1989, at Ft. McMurray in Northern Alberta, Canada, the HASDrive system was tested by the Alberta Oil Sands Technology and Research Authority, and was proven to be successful.